Softail - the sunset cruise that the watersports guys offer at CSS is on a small sailboat (like one of the Hobie Cats). One of our friends did this sunset cruise when we were there 2 years ago. At that time, it was $100 and included champagne. What was nice is that it was just the couple and the captain.
But it is true that they cannot bring a large catamaran close enough to shore for boarding at CSS because of the reef. The concierge can arrange for a cat cruise if you have you heart set on one. That is the beauty of Couples - each resort is different and offers slightly different amenities.